Colloid Blocking And Mechanism Of Bacteria On Uranium Ore Heap Leaching Process

With the rapid development of modern nuclear industry, uranium as an importantenergy fuel was gradually depleted, which has resulted the accumulation of low-gradeuranium tailings, and there were also large number of uranium existed in the tailings,which would bring the persistence of radioactivity hazards to the natural environmentand human health hazards. Bioleaching technology due to its advantages such aseconomic, environmental and other advantages have been widely used in tailingsresearch in the study. But the bioleaching of uranium tailings was a very complexphysical, chemical and biological process. The colloid would existed in the leachingsystem, which would retard the leaching of uranyl ion, resulting the low leaching rate,long leaching cycle, economic burden and environmental pressure. Therefore, it wasvery meaningful to study the effect of various factors on the formation of colloid andthe retard mechanism of colloid. In this paper, in order to cultivate the bacteria andstudy the mining research, uranium tailing taken from south China was used as theresearch object, the Acidithiobacillus thiooxidans (At.f) used in experiment was takenfrom the School of Nuclear Resources and Nuclear fuel Engineering, University ofSouth China.On the enrichment cultivation test, the growth activity of At.f was investigated bystudy the effect of the temperature and concentration of sulfuric acid. Test resultsshowed that the optimum culture conditions of At.f were: temperature was30℃,concentration of sulfuric acid was2.5g/L, and the growth cycle was shorter.The static leaching assisted bacteria test was held in this paper, it studied theinfluence of temperature, concentration of sulfuric acid and dosage of germ solutionon the formation of colloid. The results showed that the mass of colloid was highestwhen the temperature was30℃and the concentration of sulfuric acid of leachant was10g/L, and it increased with the dosage of germ solution.On the dynamic column leaching assisted by bacteria experiment, the pH、Eh、uranium concentration、mass of colloid and uranium content on colloid of leachatewere investigated under the different concentration of sulfuric acid and oxidant. Theresults showed that the pH was decreased rapidly, and then remained stable; the Ehincreased firstly and then decreased; the U concentration decreased rapidly, and then remained stable. The trend of uranium content on colloid change was similar with Uconcentration. Compared with bacteria assisted and leaching without bacteria assisted,the pH, Eh and U concentration were higher than which without bacteria assisted. Theresults indicated that At.f has a promotion to the leaching of uranium, and the oxidantH2O2could promote dissolution of ores.The SEM/EDS and FITR analysis were used to discuss the mechanism of colloidretard. According to the SEM/EDS spectrogram, the surface of colloid was uneven,rugged with lots of flaky crystal crosslinking on it, the U characteristic peak appearedin it, there were lots of organic groups such as–OH,–COOH and–NH2by analysis ofRITR spectral. The retardation was main caused by bacterial secretion, metabolismwhich could form macromolecular substance, and the state of colloid could turn intogel from sol by the flocculation, precipitation. Both of macromolecular substance andcolloid might block the space of particles and capillary frature to hinder uranyl ionsmigration into the solution.The results showed that the mechanism of colloid maybe because the largesurface area and the complex reaction between U and the function groups.